Pervasive Developmental Disorder (PDD) are a spectrum of serious disorders of childhood, affecting all areas of development and leading to severe lifelong functional impairment. Recent theory about these disorders suggests that the social deficit may be a primary feature, making its investigation central to progress in understanding etiology and intervention. Furthermore, the PDD children are a heterogeneous group, so that investigation of clinical subtypes is also a key to progress in understanding these disorders. The proposed project is one of a series by the present investigator which attempt to elucidate key questions about the social deficit in PDD children, the current project, two subtypes of PDD children are identified: those will specific social-cognative deficits and those whose social cognition is consonant with their mental age; the subtypes differed in social behavior but not in mental age. The proposed project will extend this investigation of the relationship between social behavior: and social cognition, and address other key issues, such as cross- situational variability and delay vs. deviance, in PDD social behavior. Subjects will be 40 PDD subjects currently enrolled in the study, forming a longitudinal sample, to investigate the stability of the social-cognitive subtypes, and 40 new PDD subjects, forming a cross-validation sample. Controls will be 80 children matched for mental age and IQ, and 40 normal children matched for Socialization Age. Subjects will be given a battery of standardized neuropsychological tests, a battery of social cognitive tests developed by the investigators, and a set of observational and interview measures of social behavior derived from the developmental, primate, clinical literatures. Behavior in the areas of social initiations, responses, attention, and affect will be studied. Data analysis will focus on the relationships between aspects of social cognition and social behavior, on clinical subtypes within the PDD groups, and on comparisons of social cognition and social behavior in the PDD and control groups.